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The velocity of a step motor can be held to a desired profile in a closed-loop system by using past performance to alter the amount of the delay given successive motor advance pulses.
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Adaptive Step Motor Control Circuit
The velocity of a step motor can be held to a desired profile in a closed-loop
system by using past performance to alter the amount of the delay given
successive motor advance pulses.
Referring to the figure, initial data concerning acceleration versus feedback
delay are loaded into a Feedback Delay Table 1 during power up of the system.
Acceleration of the stepper motor is measured through an Up-to-Speed Detector
2 and combined with Feedback or Timing signals at AND gate 3 to activate the
Accelerate Data Counter 4. The motor is monitored from start to a
predetermined stepping rate and may be accomplished through an acceleration-
time measurement or displacement measurement, such as the count of feedback
pulses or motor steps. These data are matched through addressing to the
proper feedback delay value in the Feedback Delay Table 1. The initial delay
value is applied to the Constant Velocity Run Control 5 to provide a referenced
feedback delay for the system based on loading present during acceleration.
Subsequent feedback pulses are delayed and the delay modified to suit load
conditions during constant velocity run at 5.
The rate of update is dependent upon system parameters and constant
velocity requirements and may be within a motor step for fine resolution or every
2, 4, 8, 16, etc., step for conventional systems. Upon initiation of stopping
control, the last updated feedback delay value is loaded into the Feedback Delay